The present invention relates generally to a quick-release retention system for bicycle wheels or other components, and is more specifically directed to the retention of a wheel using a twist-to-lock configuration for securing a non-cylindrical axle to thru-axle fork dropouts.
Quick-release retention systems, particularly for use with bicycles, have been commonplace for many years. These quick-release retention systems allow for rapid connection (or disconnection) of a portion of the bicycle, such as a wheel to a fork, without the need for specialized tools. While the most common application of quick-release devices is for the securing of a bicycle wheel to the fork or frame of the bicycle, quick release devices are also used for other applications, such as securing a bicycle seat post to a seat tube of the bicycle frame.
While various types of quick-release retention systems have been devised, the most commonly used of these devices includes a 9 mm threaded skewer having a lever on one end and a fixed stop, such as a tightening nut, on the other end. The lever acts on a cam to exert a tightening force that is a function of both the geometry of the cam and the manual pre-adjustment of the center distance between the cam and the tightening nut, wherein the center distance is adjusted by the manual manipulation of the tightening nut. The tightening force is obtained by folding the lever in the direction of the skewer, from an open position to a closed position. The user must manually adjust the center distance by adjusting the tightness of the tightening nut until the lever is able to be folded such that the cam can be driven to provide a sufficient tightening force on the skewer.
Unfortunately, these conventional quick-release retention systems pose a number of problems. One major problem is that the tightening force on the skewer is almost entirely dependent upon the center distance adjustment made by the user upon installation of the wheel or other component. It is likely that the adjustments made by the user are inconsistent between different activations of the quick-release retention system, and these inconsistencies can cause possible component wear concerns. For example, if the center distance is adjusted to be too long, the tightening force may be insufficient, and the component (such as a wheel) may not adequately engage with the fork or bicycle frame, thereby causing the operator to readjust the quick-release system by releasing the quick-release and readjusting the tightening nut. On the other hand, if the center distance is adjusted to be too short, the axial traction force on the skewer may be too great, thereby risking breakage of the skewer or another element of the quick-release retention system. Furthermore, an overly-tightened skewer may produce compression forces on the hub bearings of a bicycle wheel, thereby causing substantial friction in the hub and potential early failure of the hub bearings. It is also common for the repeated tightening of the system to cause wear or galling on the various components, such as the bicycle hub and fork, with each application of the cam. In view of these potential issues with conventional quick-release retention systems, it is clear that the user-controlled tightening may lead to component wear issues, and at the very least results in substantial trial-and-error by the user in order to achieve the correct tightening force.
Yet another disadvantage related to the conventional quick-release retention systems is that the 9 mm skewers have a cylindrical cross-sectional shape which, when applied with bicycle wheels, are only compatible with fork dropout slots having similarly rounded configurations. However, some bicycle forks, in particular suspension forks used on off-road bicycles, have been redesigned to provide a non-cylindrical “thru-axle” configuration. Thru-axle configurations comprise substantially-enclosed, non-cylindrical dropouts, as opposed to conventional dropout slots. These changes came about due to the need to maintain torsional stiffness between the opposing fork legs. The rough terrain and aggressive, high-speed riding associated with off-ride bicycling leads to substantial torsional forces being exerted on the respective fork legs. It was found that using 20 mm axles having non-cylindrical end portions engaged with the substantially-enclosed, non-cylindrical dropouts of the forks effectively created a stiffer junction between the axle and the dropouts, thereby improving the torsional stiffness of the fork. The 20 mm axle configuration, however, is not compatible with the conventional quick-release systems known in the art, and thus the “thru-axle” configuration is typically be secured to the fork using alternative means, such as threaded bolts at each end of the axle. Such a configuration may necessitate special tools to disengage the wheel from the fork, causing the user to expend a great deal of time and effort. Furthermore, the 20 mm axle design is over-sized for many applications of off-road bicycling, thereby unduly increasing the weight and cost of the axle systems.
It would therefore be desirable to have a quick-release apparatus capable of securing a bicycle wheel to the fork or frame of the bicycle without the need for manual adjustment of the center distance between a cam-action lever and a threaded tightening nut. It would also be desirable to incorporate such a quick-release apparatus using a thru-axle configuration having a non-cylindrical interface such that torsional stiffness of the fork is maintained.